A lockdown at Yale University was lifted Monday afternoon, hours after someone anonymously told a 911 dispatcher that his roommate was coming to the southern Connecticut university to shoot people, authorities in New Haven said.

No gunfire and no injuries were reported. Most of Yale's schools already were out for Thanksgiving recess, but some students and staff remained, and the school sent e-mails and texts asking them to stay in locked rooms or offices.

At least one person subsequently reported seeing somebody with a weapon on or near campus, though police were trying to determine whether the sighting was of an investigating police officer, New Haven Police Chief Dean Esserman said Monday afternoon.

"Nobody has been hurt. Nobody has been apprehended with a gun. But in this day in age, when there is a call, it behooves us to overreact and not underreact," said Esserman.

"Though it is starting to tilt in the direction of an innocent mistake, it started with a purposeful and malicious call," the police chief told reporters.

"And the New Haven police are going to track down the person who made that call. We're going to find the person who made that call, and we're going to put handcuffs on the person who made that call," he said.

The shelter-in-place order slowed officers' room-to-room searches of dorms and other buildings, because the people inside often weren't immediately opening doors for the police, not trusting that the police had come to check, according to New Haven police Officer David Hartman.

Many of the doors, he said, didn't have didn't have peepholes, so officers were taking their time persuading the occupants.

"If Yale were in full session right now, this certainly would be a tougher job for law enforcement," Hartman said.

Police said someone called 911 from a pay phone around 9:30 a.m. and matter-of-factly said his roommate "was on his way to Yale university to shoot people," Hartman said.

Investigators didn't know who the caller was or who the supposed roommate is, he said. He wouldn't comment on whether the call might be a hoax.